Engine for leisure vehicle

ABSTRACT

An engine for a leisure vehicle including a crank chamber in which a crankshaft is disposed, a transmission chamber in which a transmission unit of the vehicle is disposed, the transmission unit having an input shaft that is coupled to the crankshaft and configured to be driven by the crankshaft, a cylinder extending from the crank chamber, and a cylinder head attached to the cylinder. The crank chamber is located above the transmission chamber, and the cylinder is disposed in such a manner that an axial direction thereof is oriented in a substantially longitudinal direction of a vehicle body of the leisure vehicle.

TECHNICAL FIELD

The present invention relates to an engine for a leisure vehicle such asa motorcycle, an all terrain vehicle, a utility vehicle, or a personalwatercraft.

BACKGROUND OF THE INVENTION

In a leisure vehicle such as a motorcycle, cylinders of an engine aretypically arranged to extend substantially vertically, namely in asubstantially upright position. Especially in a multi-cylinder engine ofthe leisure vehicle, the cylinders extending substantially verticallyare arranged in-line transversely, i.e., in a width direction of avehicle body of the vehicle (see Japanese Laid-Open Patent ApplicationPublication No. Hei. 5-79347). Such a transverse-mounted in-line engineis able to advantageously reduce a mechanical loss, because a drivesystem such as a valve system has a simple construction, in contrast toa V-type engine in which cylinders are arranged in V-shape. Nonetheless,when a transverse-mounted in-line engine is equipped in a motorcycle,the longitudinal direction of the cylinders is in the verticaldirection, and a projected area of the engine as viewed from the front,that is, a frontal-projected area of the engine, increases, and as aresult air resistance increases.

In a transverse-mounted in-line engine that employs a water coolingsystem, a space between a radiator disposed forward of the engine and afront end of the engine becomes small. To extend an exhaust pipe from anopening end of an exhaust port of the engine that opens forward, it isnecessary to curve the exhaust pipe from forward to downward and fromdownward to rearward with small curvature radiuses. In this case, apressure loss and hence a fluid resistance of the exhaust pipe increase,decreasing exhaust efficiency. In addition, cooling efficiency of theradiator is likely to decrease because the radiator is subjected to heatradiated from the exhaust pipe located behind the radiator. If theexhaust pipe or the engine (cylinder, etc.) is positioned behind andnear the radiator, an amount of cooling air flow passing through theradiator from forward to rearward decreases, decreasing coolingefficiency of the radiator.

Since the cylinders are arranged to extend substantially vertically inthe above transverse-mounted in-line engine, a vertical dimension of theengine increases, and thus, a vertical space in an area where the engineis disposed is limited.

In an engine including the cylinders arranged to extend substantiallyvertically, pistons vertically reciprocate, causing vertical vibrationto occur in the engine. A rider riding on the vehicle feels the verticalvibration. To reduce the vertical vibration, some engines have acounterweight mounted to counteract the reciprocation of the piston. Insuch an engine, a weight of movable components increases, causing slowacceleration and deceleration. This is unfavorable to a high-speedengine which requires high-speed response.

In motorcycles, if the position of the engine is greatly changed tosolve the above mentioned problem, then the center of gravity of themotorcycle is correspondingly changed. If the center of gravity of theengine is greatly changed, then braking characteristics or corneringcharacteristics of the motorcycle may change. For this reason, theability to change the position of the engine is limited.

SUMMARY OF THE INVENTION

The present invention addresses the above described conditions, and anobject of the present invention is to provide an engine for a leisurevehicle that is able to decrease a frontal-projected area of the engineand to improve exhaust efficiency and air-intake efficiency withoutsubstantially changing the center of gravity of the engine with respectto a vehicle body of the leisure vehicle.

According to the present invention, there is provided an engine for aleisure vehicle comprising a crank chamber in which a crankshaft isdisposed; a transmission chamber in which a transmission unit of thevehicle is disposed, the transmission unit having an input shaft that iscoupled to the crankshaft and configured to be driven by the crankshaft;a cylinder extending from the crank chamber; and a cylinder headattached to the cylinder; wherein the crank chamber is located above thetransmission chamber, and the cylinder is disposed in such a manner thatan axial direction thereof, i.e., a reciprocation direction thereof, isoriented in a substantially longitudinal direction of a vehicle body ofthe leisure vehicle, i.e., direction in which the leisure vehicle istraveling. The axial direction of the cylinder may be substantiallyhorizontal or may be tilted upward to form a predetermined angle fromhorizontal on the cylinder head side.

In the engine for the leisure vehicle, since the axial direction of thecylinder is oriented in the substantially longitudinal direction of avehicle body of the leisure vehicle, the vertical dimension of thecylinder can be reduced. Therefore, a projected area of the engine asviewed from forward, that is, a frontal-projected area, can be reduced.The leisure vehicle equipped with the engine constructed above is ableto reduce air resistance during travel. In addition, if required, aminimum ground clearance of the leisure vehicle may be increased. Thisis favorable to an off-road motorcycle.

In the above construction, the crankshaft disposed in the crank chamberis located higher but the center of gravity of the cylinder and thecylinder head is located lower. Therefore, the center of gravity of thewhole engine is substantially identical to that of the conventionalin-line engine. So, the rider is able to enjoy travel as in theconventional motorcycle. In addition, since heavy components such as thecylinder head, the crankshaft and the like are positioned near thecenter of gravity of the whole engine, the rider is able to easily steerthe motorcycle.

In the above construction, since the reciprocation direction of thepiston substantially conforms to the longitudinal direction of thevehicle body of the leisure vehicle, the rider feels the vibration ofthe engine less. Generally, the rider riding on the motorcycle is ableto feel vibration generated in the vertical direction but is lesssensitive to vibration generated in a forward and backward direction.So, a counterweight mounted in the conventional engine to reduce thevertical vibration may be in some cases omitted, so that a weight of themovable components is reduced. As a result, the engine improvesresponsiveness and becomes lightweight.

In the above structure, by orienting the exhaust port of the cylinderhead downward, the exhaust pipe having a rear end portion extendingrearward can be curved with a large curvature radius and a small bendingangle. Thereby, the pressure loss of the exhaust pipe can be reduced,and the exhaust efficiency of the engine can be improved. By orientingthe intake port of the cylinder head upward and by disposing theair-intake device, for example, a throttle body, above the engine, theair-intake device can be coupled to the intake port of the cylinder headso as to form a straight air-intake passage extending substantiallyvertically. As a result, air-intake resistance can be reduced andair-intake efficiency of the engine can be improved.

Furthermore, in the above structure, a region of the engine having alargest width, where the crankshaft is mounted, is located higher, and alower part of the engine can be formed to have a smaller width, incontrast to the conventional in-line engine. Therefore, in themotorcycle, a larger bank angle can be obtained.

The leisure vehicle may be a motorcycle, and the cylinder may bedisposed in such a manner that the axial direction thereof issubstantially parallel to a longitudinal direction of a main frame ofthe motorcycle in a side view, the main frame being configured to extendabove the engine in a longitudinal direction of the motorcycle. In sucha construction, since the vibration of the engine is absorbed by themain frame of the motorcycle having high rigidity and is therebyreduced, the rider is less sensitive to the vibration.

The engine may further comprise an auxiliary device of the engine, forexample, a turbo charger, that is disposed in a space formed below thecylinder head and forward of the transmission chamber. Thus, the spaceformed below the cylinder head and forward of the transmission iseffectively utilized. Especially in the engine in which the exhaust portof the engine is oriented downward, if the turbo charger is disposedbelow the cylinder head and forward of the transmission chamber, andtherefore is located near the exhaust port of the engine, then theexhaust gas is efficiently guided to the turbo charger. If a catalyticdevice for cleaning the exhaust gas is disposed below the cylinder headand forward of the transmission chamber, then exhaust gas with anelevated temperature may be introduced into the catalytic device. As aresult, the catalytic device is able to clean the exhaust gaseffectively.

The auxiliary device may be at least one of the catalytic device forcleaning an exhaust gas emitted from the engine, the turbocharger, astarter motor, a generator, a battery, an oil cooler, an oil filter, anair filter device, and an oil tank. Alternatively, at least onecomponent other than these types of auxiliary devices may be disposedbelow the cylinder head and forward of the transmission chamber.

The main frame of the motorcycle may include a monocoque frame having ahollow space in which an air box is disposed. Fresh air may be suppliedto the air-intake device through the air box and an intake pipe, and anend of the intake pipe that is located on an opposite side of theair-intake device is opened in the air box. In this construction, thehollow space of the frame is effectively utilized.

The engine may be an in-line multi-cylinder four-cycle engine.

An exhaust port may be formed on a lower region of the cylinder head andan intake port may be formed on an upper region of the cylinder head.Or, the exhaust port may be formed on the upper region of the cylinderhead and the intake port may be formed on the lower region of thecylinder head. In this construction, the exhaust pipe, which has a rearend portion extending rearward, can be curved with a large curvatureradius and with a small bending angle.

The transmission chamber and the crank chamber located thereabove may beformed in a case having a transmission case portion forming an outershell of the transmission chamber and a crankcase portion forming anouter shell of the crank chamber, and these chambers may be spatiallyconnected to each other. A lid member may be removably attached to anopening that is formed on a rear end surface of the transmission caseportion of the case so as to face the crank chamber. The crankcaseportion of the case may have a parting plane configured to pass througha center of the crankshaft of the engine. In this construction, theengine can be easily assembled and disassembled. As a result,productivity of the engine increases and maintenance of the enginebecomes easy.

The engine may be an in-line multi-cylinder four-cycle engine. A drivencam sprocket may be mounted on the camshaft in an interior of thecylinder head and positioned closer to a center of the engine than anend cylinder located at an end in the width direction of the engine, adrive cam sprocket may be mounted on a cam drive shaft disposed to bespaced forward apart from the crankshaft of the engine, and a chain maybe installed around the driven cam sprocket and the drive cam sprocketto allow a drive force to be transmitted from the cam drive shaft to thecamshaft through the chain. In this construction, a cam chain tunnel orthe like formed at a side end region of the conventional multi-cylinderengine may be omitted. As a result, the width of the engine or thecylinder head can be reduced.

The drive force may be transmitted from the crankshaft to the cam driveshaft through the input shaft of the transmission.

The above and further objects and features of the invention will morefully be apparent from the following detailed description withaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view schematically showing a construction of an enginefor a motorcycle according to an embodiment of the present invention;

FIG. 2 is a side view schematically showing a construction of an enginefor a motorcycle according to another embodiment of the presentinvention, in which an axial direction of cylinders is horizontal;

FIG. 3 is a front view schematically showing a construction of theengine of FIG. 1;

FIG. 4 is a side view of a motorcycle in which the engine of FIG. 1 ismounted;

FIG. 5 is a front view of the motorcycle of FIG. 4;

FIG. 6A is a front view of an engine of FIG. 6B, a cylinder head coverof which is removed;

FIG. 6B is a side view schematically showing an engine equipped with acamshaft drive system different from that illustrated in FIG. 1;

FIG. 7 is a side view of a motorcycle having a frame different from thatof the motorcycle of FIG. 4, in which the engine of the presentinvention is mounted;

FIG. 8 is a side view of an off-road type motorcycle in which the engineof the present invention is mounted;

FIG. 9 is a side view of an all terrain vehicle in which the engine ofthe present invention is mounted;

FIG. 10 is a side view of the engine according to another embodiment,enabling easy assembly and disassembly of the engine;

FIG. 11 is a side view schematically showing a construction of theengine according to another embodiment;

FIG. 12 is a side view schematically showing a construction of aconventional engine for the motorcycle; and

FIG. 13 is a front view schematically showing the conventional engine ofFIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an engine for a leisure vehicle according to embodiments ofthe present invention will be described with reference to theaccompanying drawings. First of all, an engine for a motorcycle which isone type of the leisure vehicle will be described.

Turning now to FIG. 1, an engine 1 is a transverse-mounted in-linefour-cylinder engine including cylinders arranged transversely, i.e., ina width direction of a vehicle body of a motorcycle having a doublecradle type frame. The engine of the present invention is not limited tothe four-cylinder engine but may be a transverse-mounted in-linetwo-cylinder engine or a transverse-mounted in-line three-cylinderengine or otherwise may be a single-cylinder engine.

As shown in FIG. 4, the engine 1 is disposed below a main frame 21 of amotorcycle 20 in such a manner that an axial direction, namely, an axisL1 of a cylinder 1C of the engine 1 is substantially parallel to alongitudinal direction of the main frame 21 in a side view. The mainframe 21 extends above the engine 1 in a longitudinal direction of themotorcycle 20. The motorcycle 20 equipped with the engine 1 of FIG. 4has the double cradle type frame, and a predetermined part thereof iscovered with a cowling.

Turning to FIG. 1, the engine 1 is integral with a transmission 5, butmay alternatively be separable from the transmission 5. In thisembodiment, a crank chamber 1B of the engine 1 is disposed substantiallyright above the transmission 5. The transmission 5 includes atransmission chamber 5C and a transmission unit having gear trains inthe transmission chamber 5C. As used herein, the term “above” is meantto include obliquely above as well as right above. To be specific, acrankshaft 1D is required to be positioned above an input shaft 5A andan output shaft 5B of the transmission 5. In this embodiment, thecrankshaft 1D in the crank chamber 1B is positioned right above theinput shaft 5A of the transmission 5. The crank chamber 1B and thetransmission chamber 5C are formed together in a case Ca which forms anouter shell of both the crank chamber 1B and the transmission chamber5C.

The cylinder 1C and a cylinder head 1H are disposed adjacent to eachother to extend obliquely forward of the vehicle body of the motorcycle20 from the crank chamber 1B so as to form an angle of about 10 to 20degrees so that the cylinder 1C is tilted slightly upward on thecylinder head 1H side. The cylinder 1C and the cylinder head 1H may bedisposed horizontally as shown in FIG. 2 or otherwise to form an anglesmaller or larger than 10 to 20 degrees. In FIG. 2, the same referencenumbers as those in FIG. 1 denote the same or corresponding parts.

An intake port 1 i is formed on an upper region of the cylinder head 1Hand an air-intake device 2, for example, a throttle body, is disposedabove and adjacent the intake port 1 i. As indicated by a broken line inFIG. 1, an air-intake passage 4 is formed to extend substantiallystraight from the air-intake device 2 to the intake port 1 i to allowfresh air to flow straight downward. In this embodiment, an injector(not shown) is attached to an interior of the air-intake device 2 or theair-intake passage 4 to inject a fuel.

An exhaust port 1 e is formed on a lower region of the cylinder head 1H.An upstream end of the exhaust pipe 3 is coupled to the exhaust port 1e. The exhaust pipe 3 is curved with a curvature radius that isapproximately four to fifteen times as large as that of the conventionaltransverse-mounted in-line four-cylinder engine and with a bendingangle, for example, of 100 degrees, which is smaller than, for example,the bending angle of about 180 degrees found in conventional engines. Adownstream end of the exhaust pipe 3 extends rearward (leftward inFIG. 1) of the vehicle body of the motorcycle 20.

The input shaft 5A of the transmission 5 is coupled to the crankshaft 1Dby a pair of gears G1 and G2. The input shaft 5A is coupled to theoutput shaft 5B of the transmission 5 by reduction gear trains (notshown) that are capable of changing a reduction gear ratio. The outputshaft 5B is coupled to a rear wheel 25 (see FIG. 4) of the motorcycle 20through a sprocket and a chain (not shown). The rear wheel 25 mayalternatively be driven by a drive shaft.

As shown in FIG. 1, in this embodiment, a generator 6 is disposedseparately in front of the transmission 5. Alternatively, the generator6 may be integral with the transmission 5 in the case Ca. Since thegenerator 6 having a relatively large weight is disposed in front of thetransmission 5, i.e., at a lower position, stability of the motorcycle20 is improved. The generator 6 may alternatively be disposed above thecrank chamber 1B, although not shown. In such a construction, so-calledgyroscopic precession caused by rotation of the generator 6 occurs nearthe rider. As a result, performance of the motorcycle 20 is improved.

As shown in FIG. 4, a swing arm 24 is mounted to a pivot hole 21B formedat a rear end of the main frame 21 of the motorcycle 20 to be verticallypivotable around a pivot shaft 22. The rear wheel 25 is rotatablyattached to a rear end portion of the swing arm 24.

The engine 1 and the transmission 5 are positioned forward of the pivotshaft 22. A drive force is transmitted from a drive sprocket (not shown)mounted on the output shaft 5B of the transmission 5, through a chain23, to a driven sprocket 25S mounted to be rotatable integrally with therear wheel 25. Thereby, the motorcycle 20 is able to travel.

As shown in FIGS. 1 and 4, in the motorcycle 20, the entire air-intakedevice 2 and ½ to ⅓ of upper portions of the cylinder head 1H and thecylinder 1C are located between right and left frame members of the mainframe 21.

The engine 1 employs a water-cooling system. As shown in FIG. 4, aradiator 8 is mounted forward of a lower portion of the cylinder head 1Hand the exhaust pipe 3 and is configured to cool cooling water that hascooled the engine 1 and has elevated in temperature by using coolingair. In the motorcycle 20 of this embodiment, as shown in FIG. 1, thereis sufficient space in a region behind the radiator 8 from an upper endof the radiator 8 to a lower end of the radiator 8. In addition, thecylinder 1C and the cylinder head 1H are not in the upright position orclose to the radiator 8, unlike in the conventional engine. In thisconstruction, during travel of the motorcycle 20, cooling air flowingfrom forward smoothly passes through the radiator 8. Thus, a highcooling effect is achieved. In FIG. 1, reference symbol F denotesforward in the direction in which the motorcycle 20 is traveling.

After lubricating and cooling the cylinder head 1H, oil returns from thecylinder head 1H toward the transmission 5 through a return pipe 9indicated by a two-dotted line in FIG. 1. The oil flows to an oil pan 5Pformed in a lower portion of the transmission 5. The oil is pumped by anoil pump (not shown) mounted inside the oil pan 5P to outflow from theoil pan 5P to components to be lubricated, such as the cylinder head 1H.When the motorcycle 20 banks to the right or to the left, the oilreserved in the oil pan 5P makes contact with gears or shafts positionedthereabove. Because the gears or the shafts that make contact with theoil rotate at a speed lower than that of the crankshaft 1D of the engine1, for example, at a speed that is about ½ to ⅓ of those of thecrankshaft 1D, mechanical loss caused by the contact with the oil issignificantly reduced in contrast to the conventional in-line engine. Inother words, since the crankshaft 1D rotating at a high speed ispositioned above and distant from the oil reserved in the oil pan 5P inthe engine 1, the crankshaft 1D or a crankweb (not shown) does notsubstantially make contact with the oil reserved in the oil pan 5P, whenthe motorcycle 20 banks greatly to the right or to the left duringcornering or the like. As a result, mechanical loss is significantlyreduced. Therefore, unlike in the conventional engine illustrated inFIG. 12, it is not necessary to provide a separating wall 100 or thelike to isolate the returned oil from the rotatable components such asthe crankshaft 1D or the crankweb.

In this embodiment, the motorcycle 20 has a double cradle type (or twintube type) main frame including the right and left frame membersbranching from the head pipe. The engine 1 may alternatively be mountedin a motorcycle having a monocoque frame. FIG. 7 shows a motorcycle 220having a monocoque frame 221.

The monocoque frame 221 is of a box-shape that has a large hollow spacetherein. An air box of an air-intake system of the engine 1 may beformed in the hollow space, and an intake pipe 2E of the air-intakedevice 2 may protrude into the hollow space to open inside the air box.An air passage 250 is formed to extend from the air box in the hollowspace to a region under a head lamp 40 to enable fresh air flowing fromforward to be actively introduced into the air box. In the engine 1 ofthis embodiment, as shown in FIG. 7, since an opening of the intake pipe2E of the intake device 2 is oriented obliquely forward, a front end ofthe fuel tank 55 can be positioned immediately behind the air-intakedevice 2. For this reason, the fuel tank 55 is able to be extendedfurther forward in contrast to the motorcycle in which the conventionalengine is mounted. This increases a volume of the fuel tank 55.

Turning again to FIG. 1, a driven cam sprocket 1 y is mounted on one endof a camshaft 1 s in the interior of the cylinder head 1H, a drive camsprocket 1 r corresponding to the driven cam sprocket 1 y is mounted onthe crankshaft 1D, and a drive chain 1 p is installed around the drivencam sprocket 1 y and the drive cam sprocket 1 r so that a drive force istransmitted from the crankshaft 1D to the camshaft 1 s through the drivechain 1 p. Alternatively, as shown in FIGS. 6A and 6B, the driven camsprocket 1 y may be mounted on a center region in a longitudinaldirection of the camshaft 1 s, the drive cam sprocket 1 r may be mountedon a cam drive shaft 36 disposed in parallel with the input shaft 5A ofthe transmission 5, and the drive chain 1 p may be installed around thedriven cam sprocket 1 y and the drive cam sprocket 1 r. In thisconstruction, the length of the crankshaft 1D can be reduced. Inaddition, a cam chain tunnel formed at a side end of the engine E may beomitted. This eliminates a part protruding laterally from the engine 1.In this construction, a chain case covering the drive chain 1 p mayserve as a return passage of the oil, instead of the return pipe 9. Asshown in FIG. 6B, a drive force is transmitted from the crankshaft 1D tothe camshaft 1 s through the input shaft 5A connected to the crankshaft1D via a pair of gears and the cam drive shaft 36 connected to the inputshaft 5A via a pair of gears and an intermediate gear.

In the motorcycle equipped with the engine 1 of this embodiment, as canbe seen from FIG. 3 or FIG. 5, a projected area of the engine 1 asviewed from forward, namely, a frontal-projected area of the engine 1 issmaller than that of the conventional transverse-mounted in-linefour-cylinder engine of FIG. 12. As can be clearly seen from comparisonbetween FIG. 3 and FIG. 13 illustrating the front view of theconventional engine, the frontal-projected area is in this embodiment,20 to 30% smaller than that of the conventional engine. For this reason,air resistance of the motorcycle during the travel can be reduced. InFIGS. 12 and 13, the same reference numbers denote the same orcorresponding parts for the sake of comparison.

In this embodiment, if the axial direction, namely, the axis L1 of thecylinder 1C is substantially horizontal, a region including the cylinderhead 1H that tends to elevate in temperature is located forward relativeto the crank chamber 1B or the like in the direction in which themotorcycle 20 is traveling, and is cooled effectively by the cooling airflowing from forward toward the motorcycle 20. In an air-cooled engine,by tilting the cylinder 1C slightly upward on the cylinder head H side,the cooling wind directly contacts the cylinder 1C.

Further, in this embodiment, when the rider banks the motorcycle 20during cornering, the crank chamber 1B which has a largest width ispositioned higher than that of conventional engine 1 of FIG. 13. As canbe seen from comparison between FIG. 3 and FIG. 13, a larger bank angleα is obtained in the motorcycle 20 of this embodiment. In thetransverse-mounted in-line four-cylinder engine, which has a largewidth, and which is typically employed in the high-speed motorcycle, thebank angle tends to be small, whereas in the engine 1 of the presentinvention, a larger bank angle α is obtained, as illustrated in FIG. 3.

In the engine 1 of this embodiment, the cylinder head 1H and thecrankshaft 1D, which has a large weight, are positioned near a center ofgravity M (see FIG. 1) of the engine 1. In this construction, since aninertia moment caused by rotation of the crankshaft 1D is generated nearthe center of gravity M of the engine 1, the rider is able to easilychange the attitude of the motorcycle 20 in the lateral direction of thevehicle body, namely, in a yawing direction, during cornering or slalom.

In the motorcycle 20 in which the engine 1 is mounted as describedabove, the reciprocation direction (direction of the line L1) of thepiston is not the vertical direction of the motorcycle 20, the rider isless likely to feel the reciprocation of the piston. In particular, byconfiguring the engine 1 such that the reciprocation direction of thepiston substantially conforms to the longitudinal direction of the mainframe 21, the vibration of the engine 1 is effectively reduced by themain frame 21, so that the rider does not feel the vibration of theengine 1. Therefore, in some cases, the counterweight (balancer device)for reducing the vibration generated in the reciprocation direction ofthe piston may be omitted. As a result, a lightweight engine isachieved. This is particularly advantageous for engines of motorcyclesfor which many attempts have been already made to reduce weight. Inaddition, since the weight of the movable components of the engine 1 isreduced by omitting the counterweight, responsiveness of the engine 1can be effectively improved.

Further, in this embodiment, since the vertical dimension of the engine1 can be decreased, the air-intake device 2 can be positioned above theengine 1 to enable fresh air (or air-fuel mixture) to flow straightdownward to be supplied to the intake port 1 i. As a result, air-intakeefficiency of the engine 1 is increased.

Because of the reduced vertical dimension of the engine 1, a minimumground clearance of the vehicle body of the motorcycle 20 can beincreased, and correspondingly the bank angle can be increased. This isadvantageous to an off-road motorcycle (off-roader) 50L illustrated inFIG. 8 or a motocross motorcycle. In FIG. 8, 1 denotes an engine and 3denotes an exhaust pipe.

In the motorcycle 20 equipped with the engine 1 of this embodiment, asshown in FIG. 1, a space is formed below the cylinder 1C and thecylinder head 1H oriented substantially horizontally in a side view,i.e., forward of the transmission 5. This space is located near theexhaust pipe 3. If a turbocharger 7, which is an auxiliary device of theengine, is disposed in this space, rather than the generator 6, handlingof the exhaust pipe 3 with respect to the turbocharger 7 becomes easy.To be specific, a connecting configuration of the exhaust pipe 3 withrespect to the turbocharger 7 becomes simple and a connecting lengththereof is reduced. Alternatively, a catalytic device for cleaning theexhaust gas, which is an auxiliary device, may be disposed in the space.In that case, the exhaust gas flowing near the exhaust port 1 e, whichis elevated in temperature, is cleaned effectively. It will beappreciated that both the turbocharger 7 and the catalytic device may bedisposed in the space. In a further alternative, auxiliary devices suchas a starter motor, a battery, an oil cooler, an oil filter, an airfilter device, or an oil tank, rather than the turbocharger 7 and thecatalytic device, may be disposed in the space.

As shown in FIG. 1, in the motorcycle 20 of this embodiment, since thecylinder 1C of the engine 1 is disposed behind the radiator 8 to besufficiently spaced apart from the radiator 8, the flow of the coolingair passing through the radiator 8 is not interrupted. Because of thesmooth flow of the cooling air, the radiator 8 is able to achieve highcooling efficiency.

As described above, in the engine 1 in which the exhaust port 1 e isformed on the lower region of the cylinder head 1H, the exhaust pipe 3is curved with a large curvature radius and with a small bending angleas illustrated in FIG. 1. Thereby, the pressure loss of the exhaust pipe3 can be decreased. As a result, the exhaust efficiency of the engine 1can be increased.

As shown in FIG. 11, in another embodiment, an exhaust port 101 e may beformed on an upper region of a cylinder head 101H and an intake port 101i may be formed on a lower region of the cylinder head 101H. In thisconstruction, an exhaust pipe 103 having a downstream end portionextending rearward can be curved with a large curvature radius and witha small bending angle, and an air-intake device 102 can be disposed in aspace formed below the cylinder head 101C and the cylinder head 101H soas to be located near the intake port 101 i. Therefore, air-intakeefficiency and exhaust efficiency of the engine 1 can be increased. Inother respects, the engine of this embodiment is similar to the engine 1of FIG. 1.

Whereas in the above embodiment, the cylinder 1C and the cylinder head1H of the engine 1 extend forward from the crank chamber 1B, they mayalternatively extend rearward. In the engine 1 having such aconstruction, a wider space is formed behind the radiator 8, and theexhaust pipe 3 can be easily guided to a rear end portion of themotorcycle 20. In addition, the fresh air blowing from forward can beeasily introduced to the air-intake device 2.

The above mentioned engine 1 can be mounted in other leisure vehiclessuch as an all terrain vehicle. Turning to FIG. 9, an ATV 150 isillustrated. As in the case of the motorcycle 20, the engine 1 of FIG. 1is mounted in the ATV 150 in such a manner that a crank chamber isdisposed on an upper side of a transmission chamber of the transmissionand an axial direction, that is, an axis of a cylinder is oriented in asubstantially longitudinal direction of a vehicle body of the ATV 150.In this construction, the engine 1 is positioned forward of a pivotshaft 122 of a swing arm 124 configured to pivotally support a rearwheel 125 of the ATV 150. Since height of the engine 1 is lowered in theATV 150 constructed above, a minimum ground clearance of the ATV 150 canbe increased. In FIG. 9, 3 denotes an exhaust pipe.

The engine 1 can be mounted in other leisure vehicles such as a utilityvehicle and personal watercraft (PWC).

Turning to FIG. 10, in an engine 101 having a construction identical tothose of the above mentioned embodiments and constructed such that thecrank chamber 1B in which the crankshaft 1D is disposed and thetransmission chamber 5C in which the transmission unit is disposed arespatially connected to each other, a crankcase portion 1T of the case Caforming the outer shell of the crank chamber 1B may be provided with aparting plane 1Z to divide the crankcase portion 1T into an upper case 1u and a lower case 1 t, a transmission case portion 5 b of the case Caforming the outer shell of the transmission chamber 5C may be integralwith a lower part of the lower case 1 t, and a lid member 47 or the likemay be removably attached to the transmission case portion 5 b of thecase Ca.

In the above constructed engine 101, rotational shafts of the crankshaft1D, a generator 6, and a balancer 39 are mounted to the crankcaseportion 1T of the case Ca by bearings. As shown in FIG. 10, the partingplane 1Z is formed in the crankcase portion 1T of the case Ca to extendcenters of the rotational shafts of the crankshaft 1D, the generator 6,and the balancer 39. In addition, an opening is formed at a rear endsurface of the transmission case portion 5 b of the case Ca to faceinside of the crank chamber 1B and the transmission chamber 5C, and thelid member 47 is removably attached to the opening by bolts 48.

The engine 101 constructed above is easily assembled and disassembled.To be specific, during assembly, the lid member 47 is removed, and therotational shafts of the crankshaft 1D, the generator 6, and thebalancer 39 are positioned with respect to the lower case 1 t or theupper case 1 u, in which state, the lower case 1 t and the upper case 1u are coupled to each other. Then, bolts 44 are tightly threaded byusing a tool through the opening of the lid member 47 to enable thelower case 1 t to be threadedly secured to the upper case 1 u. With thelower case 1 t secured to the upper case 1 t, the rotational shafts ofthe crankshaft 1D, the generator 6, and the balancer 39 are rotatablymounted to the crankcase portion 1T of the case Ca by bearings.Thereafter, the lid member 47 is attached to close the opening by thebolts 48, thus completing assembly. The engine 101 is able to bedisassembled in a reversed order.

As shown in FIG. 10, a parting plane 1X is formed at an upper end of anoil reservoir 1 q formed at a lower end portion of the engine 101, andthe oil reservoir 1 q is removably attached to a lower end of thetransmission case portion 5 b of the case Ca integral with the lowercase 1 t by a plurality of bolts 49. In this construction, by removingthe bolts 49, the oil reservoir 1 q is removed to enable an operator tovisually check the interior of the transmission 5 from below. In FIG.10, reference symbol 5A denotes an input shaft of the transmission 5, 5Bdenotes a change drum shaft, 27 denotes a water pump, and 29 denotes anoil cooler.

As this invention may be embodied in several forms without departingfrom the spirit of essential characteristics thereof, the presentembodiments are therefore illustrative and not restrictive, since thescope of the invention is defined by the appended claims rather than bythe description preceding them, and all changes that fall within metesand bounds of the claims, or equivalence of such metes and boundsthereof are therefore intended to be embraced by the claims.

1. An engine for a leisure vehicle comprising: a crank chamber in whicha crankshaft is disposed; a transmission chamber in which a transmissionunit of the vehicle is disposed, the transmission unit having an inputshaft that is coupled to the crankshaft and configured to be driven bythe crankshaft; a cylinder extending from the crank chamber; and acylinder head attached to the cylinder; wherein the crank chamber islocated above the transmission chamber, and the cylinder is disposed insuch a manner that an axial direction thereof is oriented in asubstantially longitudinal direction of a vehicle body of the leisurevehicle.
 2. The engine for a leisure vehicle according to claim 1,wherein the cylinder is disposed in such a manner that the axialdirection thereof is substantially horizontal.
 3. The engine for aleisure vehicle according to claim 1, wherein the cylinder is disposedin such a manner that the axial direction thereof is oriented to betilted upward to form a predetermined angle from horizontal on thecylinder head side.
 4. The engine for a leisure vehicle according toclaim 3, wherein the leisure vehicle is a motorcycle, and the cylinderis disposed in such a manner that the axial direction thereof issubstantially parallel to a longitudinal direction of a main frame ofthe motorcycle in a side view, the main frame being configured to extendabove the engine in a longitudinal direction of the motorcycle.
 5. Theengine for a leisure vehicle according to claim 4, further comprising:an auxiliary device of the engine that is disposed in a space formedbelow the cylinder head and forward of the transmission chamber.
 6. Theengine for a leisure vehicle according to claim 5, wherein the auxiliarydevice is at least one of a catalytic device for cleaning an exhaust gasemitted from the engine, a turbocharger, a starter motor, a generator, abattery, an oil cooler, an oil filter, an air filter device, and an oiltank.
 7. The engine for a leisure vehicle according to claim 4, furthercomprising: an air-intake device disposed above the cylinder head. 8.The engine for a leisure vehicle according to claim 7, wherein the mainframe of the motorcycle includes a monocoque frame having a hollow spacein which an air box is disposed; and wherein fresh air is supplied tothe air-intake device through the air box and an intake pipe, and an endof the intake pipe that is located on an opposite side of the air-intakedevice is positioned in the air box.
 9. The engine for a leisure vehicleaccording to claim 4, wherein a crankshaft of the engine is positionedforward of a pivot shaft of a swing arm of the motorcycle.
 10. Theengine for a leisure vehicle according to claim 1, wherein the engine isan in-line multi-cylinder four-cycle engine.
 11. The engine for aleisure vehicle according to claim 1, wherein an exhaust port is formedon a lower region of the cylinder head and an intake port is formed onan upper region of the cylinder head.
 12. The engine for a leisurevehicle according to claim 1, wherein an exhaust port is formed on anupper region of the cylinder head and an intake port is formed on alower region of the cylinder head.
 13. The engine for a leisure vehicleaccording to claim 1, wherein the transmission chamber and the crankchamber located thereabove are formed in a case having a transmissioncase portion forming an outer shell of the transmission chamber and acrankcase portion forming an outer shell of the crank chamber and arespatially connected to each other; wherein a lid member is removablyattached to an opening that is formed on a rear end surface of thetransmission case portion of the case so as to face the crank chamber;and wherein the crankcase portion of the case has a parting planeconfigured to pass through a center of the crankshaft.
 14. The enginefor a leisure vehicle according to claim 1, wherein the engine is anin-line multi-cylinder four-cycle engine; and wherein a driven camsprocket is mounted on a camshaft in an interior of the cylinder headand is positioned closer to a center of the engine than an end cylinderlocated at an end in the width direction of the engine, a drive camsprocket is mounted on a cam drive shaft disposed to be spaced forwardapart from the crankshaft of the engine, and a chain is installed aroundthe driven cam sprocket and the drive cam sprocket to allow a driveforce to be transmitted from the cam drive shaft to the camshaft throughthe chain.
 15. The engine for a leisure vehicle according to claim 14,wherein the drive force is transmitted from the crankshaft to the camdrive shaft through the input shaft of the transmission.